Hey bud
OK well 1st off the 6870 prices won't drop...or not for at least another year or so.
Even with the new card launching you'll still see how suppliers and resellers punt the same prices, main reason for this, the new cards are quite pricey so they reckon they'll still sell some of the older cards at current prices. I have run many crossfire setups and I am in the process of getting a 2nd 7970 to cf right now, the main issue is always issues with games that have compatibility issues ect.
Honestly I would say sell you're 6870, save up a bit of cash and try get yourself a 7950. They are beastly cards, been reading reviews when I get a chance.
As for kepler...No one knows, there is just way to much secrecy involved with it, so I can't give you an answer. Honestly I doubt they'll be able to keep up with the 7xxx amd cards, but no one knows. As for release on them, apparently the mid range cards will launch april this year.